Expressed at relatively low levels in colonic mucosa, ovary, peripheral leukocytes, prostate and small intestine, and at higher levels in spleen, testis and thymus. Expressed in multiple regions of the brain and CNS including amygdala, caudate, corpus callosum, hippocampus, substantia nigra and subthalamic nucleus. Isoform 1 is the predominant isoform in monocytes, macrophages and neutrophils, isoform 2 is most strongly expressed in peripheral blood leukocytes and quiescent CD34 positive cells, and isoform 3 is expressed at low levels in all hematopoietic cell types. Expression is frequently reduced in non-small-cell lung carcinomas (NSCLC) due to hemizygous gene deletion, strongly suggesting that this locus is haploinsufficient for tumor suppression. Loss of this locus frequently occurs in tumors which retain wild-type CDKN2A/ARF and p53/TP53 loci. Hemizygous gene deletion has also been observed in leukemic blasts from patients with abnormalities of the long arm of chromosome 7.